The invention relates generally to optical chemical sensors and more particularly to fiber optic chemical sensors.
A wide variety of optical chemical sensors, have been proposed to measure a variety of chemical species. For example, U.S. Pat. Nos. 4,929,049 and 5,026,139 to Klainer, et al describe chemical sensors for hydrocarbons using thin film metal clads on an optical fiber.
However, to develop a practical, reliable sensor for long-term field use requires a sensor configuration which eliminates problems of variations in the components, particularly the source, due to aging, temperature changes, etc. The output of the sensor should vary only as a function of the species being detected and not because of variations in internal or external factors. U.S. Pat. No. 5,094,958 to Klainer et al shows one approach which produces two responses, only one of which is analyte specific. The other only depends on external factors so the ratio is self-compensating.